Marked card

From MTG Salvation Wiki

A marked card is a card in a deck that can be identified by some means other than looking at its face. Protective sleeves can also be considered marked in a similar manner. Marked cards are illegal in all tournament play because there may be the chance that the player is cheating by knowing all the marks and may predict his/her draws.

Some examples of features that make a card "marked" include excessive wear, patterned wear, pen markings, card curvature or card-back color saturation. Card curvature can matter when using foiled premium cards, as early foil cards would warp differently than normal cards. Card-back color saturation can matter when using cards from different sets, especially when combining older and newer cards. Older cards tend to have a more varied and lower saturation to the card back while newer cards have a more homogeneous and higher saturation to them.